{
  "bibcode": "2025GCN.38775....1S",
  "subject": "GRB 250101A: Swift/UVOT Detection",
  "circularId": 38775,
  "eventId": "GRB 250101A",
  "submitter": "Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>",
  "format": "text/plain",
  "submittedHow": "web",
  "body": "M. H. Siegel (PSU) and K. L. Page (U. Leicester)\nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 250101A\n133s after the BAT trigger (Page et al., GCN Circ. 38752).\nA fading source consistent with the XRT position (Goad et al., GCN Circ. 37761)\nand the previously reported optical source, since confirmed by\nmultiple observations (Li et al., GCN Circ. 38753; Mohan et al., GCN\nCirc. 38754; Zhu et al., GCN Circ., 38755; Wu et al., GCN Circ 38578;\nMoskvitin & Spiridonova, GCN Circ. 38762; Odeh et al., GCN Circ 38763;\nHu et al., GCN Circ. 38764; D'Avino & L. Izzo, GCN Circ. 38768;\nEscudero-Coca, GCN Circ. 38769; Leonini et al., GCN Circ. 38771)\nis detected in the initial UVOT exposures.\n\nThe preliminary UVOT position is:\n    RA  (J2000) =  02:28:16.47 =  37.06864 (deg.)\n    Dec (J2000) = +19:11:39.6  =  19.19433 (deg.)\nwith an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence).\n\nPreliminary detections and 3-sigma upper limits using the UVOT photometric system\n(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: \n\nFilter         T_start(s)   T_stop(s)      Exp(s)           Mag\n\nwhite              133          283          147         18.03 +/- 0.05\nv                  620          813           39         18.10 +/- 0.28\nb                  546          738           39         18.66 +/- 0.21\nu                  291          540          246         17.93 +/- 0.08\nw1                 670         5019          235        >19.8\nm2                4614         4814          197        >19.1\nw2                 596         4404          216        >18.9\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.164 in the direction of the burst\n(Schlegel et al. 1998).\n\nWe note that the lack of detection in the NUV bands for this bright burst would\nbe consistent with the redshift of z=2.49 reported by Zhu et al. (GCN Circ. 38759).",
  "createdOn": 1735801885813
}